This disclosure relates generally to methods and systems for color management in image/text printing or display systems, and more particularly to a system and method for automatically achieving spot color production through use of a plurality of gain matrices per spot color in determining spot color coordinates. Furthermore, this disclosure provides a means for mapping out-of-gamut target spot colors substantially near a boundary of the gamut of an image output device, such as a printer or display.
To meet customer demand, the commercial printing industry requires the capability of producing spot colors accurately and consistently. Spot colors can be defined as a fixed set of colors which may be Pantone® colors, customer logo colors, colors in a customer's proprietary marked patterns, or customer defined colors in the form of an index color table. Spot colors are often used, or can be used, for large background areas, which may be the most color critical portion of a particular page. Consistent color in these areas may determine the difference between success or failure in meeting customer requirements.
A goal of the disclosed system and method is to transform the current production print practice by providing an automated approach to the printing of spot colors. Because imaging can occur over a variety of different printing systems and practiced by a variety of different clients and customers, the colors may not always be consistent or accurate. Existing spot color editors utilize a manual approach to the adjustment of CMYK recipes of spot colors prior to raster image processing (RIPing). For example, the document creator may select a Pantone color for application in specific areas through a user interface on a printing device or computer monitor, such as that available on the Xerox® DocuSP® Controller. The Pantone-provided CMYK recipe for the selected printer is obtained from a look-up table. Prior to RIPing the document in the printer, the operator has the option of entering a spot color editor function and specifying an alternative CMYK recipe to achieve the desired color. The document is then RIPed and then printed using the spot color editor recipes where specified, and Pantone recipes otherwise.
Notably, the algorithms used in such prior art devices require the use of a pre-calculated single gain matrix per spot color as inputs. Gain matrices are obtained using the printer Jacobian matrix and MIMO pole-placement algorithms. Since these matrices are calculated offline during the printer characterization process, the convergence of spot colors to achieve desired accuracy can vary depending on the machine state. Also, the state feedback design may not perform as well as desired for colors near the boundary and the deltaE2000 convergence criteria cannot be easily defined while selecting proper gain matrices since the prior art design uses the CIELab convergence criteria. The computation of deltaE2000 number provides an improved method for comparing color differences in perceptual space. Therefore, it is highly desired to establish the convergence criteria in such a way that the deltaE2000 value for each color is minimized using the minimum number of algorithm iterations. Consequently, it would be desirable to have an automated system that provides improved color performance through the use of a plurality of gain matrices per spot color in determining spot color coordinates.